DESCRIPTION (provided by application): In the two hermaphrodite specific neurons (HSNs) of C. elegans, serotonin synthesis and axon outgrowth occur at fixed times during larval development, but the mechanisms underlying their temporal regulation are largely unknown. Genes that control developmental timing in hypodermal tissues have been identified and ordered into a dedicated heterochronic pathway, and one of these genes, lin-14, controls timing of postmitotic development in the DD neuron subtype. The hypothesis that heterochronic genes together with neuron-specific regulators temporally control HSN differentiation will be tested by: 1) Investigating the effects of mutation or RNAi knockdown of known heterochronic genes on timing of serotonin synthesis and axon outgrowth in the HSNs, and 2) Identifying new genes that regulate timing of HSN differentiation using a Mos1 transposon screen and a candidate gene approach. These studies will enhance our understanding of genetic mechanisms of temporal regulation in C. elegans neurons, and may lead to new insights pertaining to the causes and potential treatments of developmental disorders in the human nervous system.